I'm considering buying Red Dead Redemption: Undead Nightmare. I found the disc for cheap, but I already own the original Red Dead Redemption.

Does Undead Nightmare include all the content from the originally released Red Dead Redemption? Or is it just the DLC and not the original storyline? I found places that say what it adds, and that it includes this and other DLC. But nothing explicitly says whether it includes the original disc of content.